Preformed abrasive article and process of making same



Aug. 4, 1936. s. ME RIAM PREFORMED ABRASIVE ARTICLE AND PROCESS OF MAKING SAME Filed Sept. 17, 1955 Patented Aug. 4, 1936 UNITED STATES PATENT OFFICE PREFOBMED ABRASIVE ARTICLE AND PROCESS OF MAKING SAME 8 Claims.

This invention relates to preformed abrasive articles and a process for making the same. More particularly the invention contemplates the provision of a novel, efficient, and economic proces for producing abrasive wheels of superior quality. According to current practice, abrasive grinding wheels are composed of grains or grit of hard abrasive material, generally oxide of aluminum or silicon carbide bonded together by a suitable bonding agent. The nature of the bonding material and its quantity determine, to a large extent, the character of the it may be put.

Both organic and inorganic bonding materials are used, the latter, however, being the most common. The usual bonding material comprises a vitrified substance resembling porcelain produced by a controlled process of heating in some form of kiln. I I

In the manufacture of vitrified abrasive articles, the abrasive grains or grits are mixed with clays of the desired qualities together with feld-' spar, fiint, or' like materials and water. The mixture is then formed into the desired shape, such as a wheel, bymolding orthe like. The wheel is then dried andplaced in a kiln. The characteristics of the wheel are controlled to some extent by varying the amount and nature of the bond 30 employed as well a'slby the subsequent heat treatmen Both continuous tunnel pottery type kilns are type and intermittent currently employed for the heat treatment of the wheels. In the tunnel type kilns, usually around four days are required to mature and cool the wheels. In the pottery type kilns, it may require as long as three weeks to produce the finished is expensive and requires a large investment. The

40 consumption of large amounts of fuel and the time factor in kiln firing are important items in the production costs because of the necessity of retaining for. long periods the arches, saggers, walls; and entire kiln at the requisite tempera- 45 ture.

It is the purpose of the present invention to completely obviate thenecessity for kiln firing in the production of vitrified abrasive wheels. By the present invention the great fuel costs incident 50 to the manufacture of vitrified abrasive wheels are reduced to aiminimum as are the labor costs and capital investment. Furthermore the production of my improved abrasive wheel is reduced to a one-day operation.

. In accordance with the present invention, the

wheel and the uses to which wheel. The use ofany kiln REISSUED heat necessary to produce the vitrified bond in the wheel is generated in the wheel itself without the application of extraneous heat such as required in kiln firing.

While the invention in its broader aspect com- 5 prehends any of many modes of generating the necessary heat to form the vitrified bond in situ in the wheel, my preferred method will be first described. In this method the abrasive grains or. grits are mixed with the necessary known ingrel0 dients to form the required bond in the finished wheel. With this mixture there is incorporated in uniformly distributed form a combustible material of such character and in such amount as to generate suflicient heat, upon burning, to 15 produce the bond in situ.

The combustible material employed must be such as will not react so vigorously as to cause violent escape of volatile products, and it must not leave any objectionable non-volatile residue in the wheel. I have found petroleum coke or coke produced from coal tar to function very satisfactorily in the process since it produces substantially no ash. Other combustible materials :possessing the above defined characteristics are, of course, suitable for use.

Because clays, feldspar, and flint form a heterogeneous system in which reaction may be slow, I prefer to use materials for forming the bond in a prefused or fritted condition so that only a relatively simple fusion is required to be eifected in the wheel. I can if desired, of course, add more readily fusible materials, such as borax, cryolite, and the like to act as a fiux.

In order to reach temperatures in the. wheel of from 1000 to 1500 0., it is necessary to use only from 4% to 8% by weight of carbon or its equivalent in the wheel when the burning is effected in an atmosphere of oxygen. Slightly more is required when the burning is efiected solely through the use of air.

It will, of course, be understood that in preforming the wheel before heat treatment, any of the conventional temporary bonding agents maybe employed such as dextrine and bakelite which burn off completely inthe heat treating step.

The character of the final wheel can be accurately controlled, as well as its porosity, by varying the nature and physical structure of the incorporated combustible material. 'For example, if finely powdered coke is used, the finished wheel will be more dense than when granular coke is used. This is due to the fact that the burning out of the combustible material 55 leaves voids in the wheel comparable in size and number with the individual elements of the combustible material employed. If a wheel of a high degree of porosity is desired, a less dense form of combustible materal is used, such for example as charcoal, which is much more bulky than coke, for a given heat development in the wheel. It is possible to use such carbonaceous materials as corn meal, cork particles, and the like. Due to the water produced in their combustion, however, it is preferable to bond the wheel weakly with water glass and then pre-char the woody materials at a low heat. This expedient need be resorted to only in the event that highly porous wheels are desired.

In preparing the mixture which is to form the final vitrified abrasive wheel, the abrasive grains are weighed together with the requisite amount of bonding material in finely divided form. There is then added a proper percentage, i. e., 4% to 8% by weight, of a selected carbonaceous fuel, usually petroleum coke. A temporary bonding material is then added and thoroughly mixed with'the other ingredients. It will be understood that this temporary bond simply acts to hold the wheel in shape during the drying and handling operations preparatory to placing it in the retort.

A suitable retort for carrying out the process of the present invention is illustrated in the accompanying drawing.

The retort embraces the outer cylinder l of thin metal and the somewhat heavier top 2 and bottom 3. The cylinder l carries annular flanges 4 and 5 at the top and bottom, respectively, adapted to cooperate with the peripheral flanges 6 and l at the top 2 and bottom 3. A suitable deformable metal washer 8 is clamped between the flanges i and 6 at the top, and a simliar washer 9 is clamped between the flanges 5 and l at the bottom. The bottom 3 may, of course,-

be permanently united to the cylinder I. As illustrated, however, both the top 2 and bottom 3 are removable by simply taking out the clamping bolts l0.

The top 2 and bottom,3 are reinforced by angle iron struts H welder. thereto. The top is provided with a central opening i2 and the bottom with an opening it. An inlet pipe M has a gastight fit with the opening 12 and is provided with valve controlled branch lines l5 and I6 for air and oxygen. There is also mounted on the line 14 a suitable pressure gauge H for observing the pressure conditions prevailing in the retort. Immediately below the opening 12 in cover 2, there is suspended by rods l8 a baiiie member [9 to prevent channeling of the incoming air or oxygen. An outlet pipe 20 for combustion gases and cooling air has a gas-tight fit in the opening 13 in the bottom of the retort. The retort carries trunnions 2! that permit it to be inverted for removal of its charge of treated wheels.

A free circularspace having a diameter somewhat greater than that of the wheels to be treated is provided at the bottomimmediately above the outlet line 20. This space is between the bottom 3 and the perforated plate or screen 22 suitably supported a few inches above the bottom. An open-ended cylinder 23 having a diameter somewhat greater than that of the wheels to be treated is disposed in concentric relation to the outer cylinder l. The annular space between the cylinders I and 23 is packed with suitable insulating material. A spark plug 24 is fitted into the cover 2, and a coil of readily ignitable thin iron wire such as a ll0-v0lt service line.

In packing a batch of wheels in the retort, a

bed of abrasive grains such as used in the wheels 5 is filled in at the bottom of the cylinder 23 and supported on the perforated plate 22. A bafile plate 21 may advantageously be set in the bed. The first green wheel containing the requisite amount of combustible material is next laid on the bed and has free abrasive grains filled in around its circumference and in it's axial opening. There is then placed over the first wheel a layer of abrasive grains having mixed therewith coke or other combustible material but no binding agents of any kind. This layer transmits combustion directly from the wheel above to the wheel below, but since it contains no bonding material, the grains remain free after the burning operation and the layer acts to keep the wheels separated as individual units. The next wheel is then laid in and the operation repeated until the retort is filled. As illustrated, the retort has a capacity of twelve wheels. The top wheel is covered with a layer of-grains and admixed coke, and there is also advantageously provided a layer of a suitable readily ignitable substance in immediate proximity to said iron wire coil 25.

When the retort is packed, the cover 2 is affixed in sealed relation thereto and oxygen supplied through the line l5. Suitable means such as a flow meter (not shown) may be provided in the lines 14 and 20 for accurately controlling the rate of flow of air or oxygen through the retort. A switch (not shown) in the spark plug circuit is next closed, which effects ignition in the retort. After ignition has been effected, excess air may be supplied through line 16 in substitution for all or a part of the oxygen being supplied through line 15. The burning takes place very rapidly and can be controlled by the pressure at which the air or oxygen is supplied and the rate of flow thereof through the retort. Ordinarily burning is complete in from twenty to thirty minutes. During this time no heat leaves the retort, and the outgoing gas remains cool and is largely CO2. Heat does not begin to escape through the retort wall until nearly an hour later. If time is not a factor, cooling is allowed to occur without acceleration and requires from twenty-four to thirty-six hours. By passing a slow stream of air through the retort, the cooling time can be reduced to around eight hours m'thout deleterious effects.

The wheels produced in accordance with the process are superior to kiln cured wheels since they are more highly porous due to their content of voids formed by the burning of the combustible material in the wheel during formation of the vitrified bond. Furthermore wheels of predetermined density can be produced.

The current difficulty of non-uniformity of wheels from one run to the next is completely overcome in my process. I need employ no temperature measuring instruments of any kind since, by precise measurement of the fuel introduced to the wheel mix and control of the flow of the gas, a consistently uniform product necessarily results.

It is possible in the molding of the wheels to form on one side thereof a thin layer of grains and admixed coke with a temporary binder only therein. The premolded wheels carrying such layers may then be rapidly placed in the retort All and, when burned, the layers are transformed into free unbonded grain layers separating the vitrified abrasive wheels.

In some instances it may be advantageous to include coke in the free grains that are packed around the periphery of the green molded wheels in the retort. This expedient furnishes additional heat and insures complete reaction at the rims of the wheels.

In the production of thin dense wheels, it is sometimes desirable to generate all the heat in the intermediate layers and surrounding grains without the necessity of incorporating the combustible material in the wheel mix.

A further modification of the process contemplates adding to the wheel mixture a sub-' stance capable of combining with various metallic oxides forming a bonding substance and then burning the suitable metal. An illustrative example comprises mixing with the abrasive grains both borax and metallic zinc and then burning the metallic zinc with a completely volatile oxidizing agent such as ammonium perchlorate or with gaseous oxygen or air. The resulting zinc oxide forms with borax a vitreous bond for the abrasive grains. This modification is not limited to this particular combination since other metals and other reactive materials, such as sodium silicate, various other silicates, meta and pyro-phosphates, and substances of like nature including oxides of non-metals such as silica, maybe used.

Having thus described my invention, what I claim is:

1. In a process for manufacturing abrasive articles, the steps 01 forming a plurality of green abrasive articles containing abrasive grains, reagents adapted upon subjection to adequate heat to form a vitreous bond between said grains, and a combustible material, placing said green articles in a retort and separating the same therein by interposed segregating layers containing a combustion supporting substance, and igniting and burning in said retort said combustible material in said articles and combustion maintaining substance in said segregating layers to thereby generate the requisiteheat within the retort to form a vitreous ,bond between the abrasive grains in said abrasive articles.

2. A process for producing abrasive articles comprising mixing suitable abrasive grains with a vitriilable bond and a combustible material sufllcient in amount to, when burned in situ, generate adequate heat within the article to effect binding of said abrasive grains by said vitrifiable bond. forming the mixture into the desired shape, igniting and burning said combustible material.

3. A process for producing abrasive articles comprising mixing suitable abrasive grains with a vitriflable bond, including in the mixture combustible material sufilcient in amount to when burned in situ generate adequate heat in said article to form a vitreous bond between said abraplurality of green wheels, placing said wheels in a sive grains and thereaiter igniting and burning said combustible material.

4. A process for producing abrasive articles comprising mixing suitable abrasive grains with a previously fused vitreous binding material in 5 iinely divided form, including in the mixture a temporary binder and a substantially non-resldue producing combustible material sufllcient inamount to, when burned in situ, generate adequate heat in the article to re-i'use said vitreous binding material, forming the mixture into the desired shape and then igniting and burning said combustible material.

5. A process for producing abrasive articles comprising mixing suitable abrasive grains with vitriflable reagents adapted upon being subjected to adequate heat to produce a vitreous bond between the abrasive grains, including in the mixture a combustible material sufllcient in amount to, when burned in situ, generate adequate 20 heat to cause said vitriflable reagents to form a vitreous bond, forming the mixture in the desired shape and then burning said included combustible material.

6. A process for producing abrasive. articles 25 comprising mixing suitable abrasive grains with reagents, capable upon being subjected to adequate heat, of reaction and fusion to produce a vitreous bond, including in the mixture a temporary binder and a substantially non-residue 30 I producing combustible material sumcient in amount to when burned in situ generate adequate heat to efiect reaction and fusion oi. said reagents to form a vitreous bond, forming the mixture into the desired shape and then burning said combustible material.

7. A process for producing abrasive wheels and the like comprising mixing suitable abrasive grains, 8. previously fused vitreous bonding material in finely divided form, a temporary binder and a substantially non-residue producing combustible material sufficient in amount to, when burned in situ, generate adequate heat to again iuse said vitreous bonding material, molding a retort with intervening layers 0! bond free abrasive grains and igniting and burning said combustible material.

8. A method for producing abrasive wheels comprising mixingsuitable abrasive grains with a vitriiiable bond and combustible material adequate in amount to generate, when burned in situ, suflicient heat to produce from the vitriflable bond a vitreous bond between said abrasive grains,

forming a plurality of temporarily bonded wheels, 55

placing said temporarily bonded wheels in a retort wherein each individual wheel is surrounded by unbonded abrasive grains similar in character to those included in the wheels and igniting and burning the combustible material in situ in the wheels in said retort to produce a vitreous bond between the abrasive grains in each wheel.

EDMUND S.MERRIAM. 

